This invention relates to means for automatically controlling sequentially actuated apparatus.
More particularly, this invention relates to interface means for interconnecting a sequentially actuated apparatus to a computer to automatically maintain at a desired level a process variable of said apparatus.
Even more particularly, this invention relates to interface means capable of interconnecting a plastics injection molding machine and a computer to automatically maintain at a specified level one of the machine's process variables such as boost pressure.
Many varieties of sequentially operated machines such as plastics injection molding machines contain a plurality of process variables which are critical to the production of a satisfactory product. With particular regard to injection molding apparatus, such variables as melt temperature, boost and clamp pressures, heat dissipation in the plasticizing mechanism, and linear movement of the ram all play an essential role in the ultimate formation of the plastic parts. Heretofore, maintaining each of these variables within the required ranges during each repetitive cycle of operation of the machine has been primarily achieved through manual control at the machine proper. Thus, an operator was required to maintain constant vigilance of each machine during its entire operation. Needless to say, such a requirement adds appreciable to both manufacturing costs and the possibilities for human error.
Methods known for automatically controlling injection molding machines to the extent that one or a few of these variables could be reasonably held within desired limits have most usually required extensive electronic circuitry of such complex nature that any cost advantage as opposed to manual control was not appreciated. Additionally, continuous maintenance of this circuitry was essential and added still further to such costs.
Consequently, there has been an increasing demand in industry for the use of relatively small computer systems to serve as control means for processes such as injection molding. Computers of this type provide a degree of reliability heretofore unknown when controlling processes of several machines at one time. Furthermore, because a single computer can be effectively utilized to control several machines, the requirement of only a single operator returns the cost advantage to the manufacturer in addition to substantially reducing the opportunities for human error. Yet, to this date there are no known methods which are relatively inexpensive and simple in operation and which can satisfactorily interconnect a small computer to a production apparatus of the type described to automatically control a process variable of the apparatus. Similarly to the electrical circuitry previously described, interface assemblies have heretofore been substantially complex and costly.
It is believed therefore that an interface means for interconnecting a computer to a sequentially operated machine which is relatively simple in operation and inexpensive to produce and is capable of positively maintaining at a desired level process variables of said machine would constitute an advancement in the art.